Motion control is an important aspect in robotic systems (e.g., involving articulated robot configurations, Cartesian robot configurations, cylindrical robot configurations, polar robot configurations, delta robot configurations, or the like or combinations thereof), numerical control (NC) machines, computerized NC (CNC) machines, and the like (generically and collectively referred to herein as “machine tools,” which can be adapted to process a workpiece). These machine tools typically include one or more controllers, one or more actuators, one or more sensors (each provided as a discrete devices, or embedded in an actuator), a tool holder or tool head, and various data communication subsystems, operator interfaces, and the like. Depending on the type and number of actuators included, a machine tool may be provided as a “multi-axis” machine tool, having multiple, independently-controllable axes of motion.
The continuing market need for higher productivity in machining and other automation applications has led to the increasing use of machine tools with various types of actuators, sensors and associated controllers. In some cases, a multi-axis machine tool (also referred to herein as a “hybrid multi-axis machine tool”) may be equipped with multiple actuators capable of imparting movement along the same direction, but at different bandwidths. Generally, one actuator (e.g., a first actuator) can be characterized as having a higher bandwidth than another actuator (e.g., a second actuator) if the first actuator can impart movement in response to a command signal having a given spectral or frequency content more accurately than the second actuator can impart movement in response to the same command signal. Often, however, the range of motion over which the first actuator can impart movement will be less than range of motion over which the second actuator can impart movement.
Deciding which components of motion should be allocated between relatively-high and relatively-low bandwidth actuators of a hybrid multi-axis machine tool is not an easy task. A common strategy involves operating one or more relatively-low bandwidth actuators to move a workpiece to be processed and/or to move one or more relatively-high bandwidth actuators to a desired location or “zone” where the workpiece is to be processed, and then hold the position of relatively-low bandwidth actuator(s) constant while operating the relatively-high bandwidth actuator(s) during processing of the workpiece. Thereafter, the relatively-low bandwidth actuator(s) are operated to move the workpiece and/or the relatively-high bandwidth actuator(s) to another “zone” where the workpiece is to be processed. This “zone-by-zone” approach (also referred to as a “step-and-repeat” approach) to motion control is undesirable because it significantly limits throughput and flexibility of the hybrid multi-axis machine tool. It can also be difficult to appropriately or beneficially define the various “zones” of the workpiece where the relatively-high bandwidth actuator(s) can be operated.
U.S. Pat. No. 8,392,002, which is incorporated herein by reference in its entirety, is understood to address the above-mentioned problems associated with implementing the “zone-by-zone” approach by processing a part description program to decompose a tool tip trajectory (on the basis of frequency) defined in the part description program into different sets of position control data appropriate for the relatively-low and relatively-high bandwidth actuators of a hybrid multi-axis machine tool. However, and as acknowledged in U.S. Pat. No. 8,392,002, when the hybrid multi-axis machine tool is configured to hold a workpiece using 5-axis CNC manipulator with two rotary axes riding on a 3-axis Cartesian stage, and includes relatively-high bandwidth actuators to move a tool tip in the 3 Cartesian axes, use of the frequency-based decomposition approach can result in errors in the angles associated with the rotary axes.